| The electromagnetic pollution is an increasingly serious problem in the modern environment,which has brought great harm to people's health and work.Microwave absorbing material is one of the main methods to solve electromagnetic interference and other problems.Inside,carbon nanotubes(CNTs)have unique electromagnetic properties owing to the special tubular structure.They have great potential in the practical application of microwave absorption.Therefore,the study of CNTs has become a new research hotspot in microwave absorption.In this paper,multi-wall Carbon Nanotube(MWCNTs)was used as absorbent and silicone rubber as matrix to prepare carbon nanotube/silicone rubber composite microwave absorbing materials.The microwave absorbing properties of the composite materials were investigated.Based on the composite materials,three kinds of microwave absorbing structures were designed to provide solutions for the future application.Firstly,the preparation method of coaxial samples composite materials,guarantees the quality of coaxial samples and improves the accuracy of extracting electromagnetic parameters of composite materials;The transmission/reflection method is used in measuring electromagnetic parameters is introduced,and carries out data processing for the measured electromagnetic parameters,obtains the suitable parameters and documents for HFSS.The principle of transmission line and its application in multi-layer structure is introduced.Secondly,coaxial samples of composite materials with carbon nanotubes mass fraction of 0.5%,1%,1.5% and 2% were fabricated,and their complex permittivity and permeability were measured by transmission/reflection method.The influence of carbon nanotubes mass fraction on electromagnetic parameters of composite materials was investigated.The microwave absorption properties of the above composite patches with 2 mm thickness were investigated.The absorption peak frequency of the composite patches with 2% carbon nanotubes mass fraction was at 10.88 GHz,the maximum loss was-28.81 dB,and the bandwidth is 9.56-12.76 GHz.The microwave absorption characteristics of carbon nanotubes(CNTs)composites with 2% mass fraction at different thickness were investigated.The loss mechanism and oblique incidence properties of CNTs/silicone rubber composite patches has been studied.Then,according to the transmission line theory,a composite structure of impedance FSS-carbon nanotubes/silicone rubber composite patches has been designed.The top layer is impedance FSS,the middle layer is honeycomb dielectric layer,and the bottom layer is carbon nanotubes 2% composite patches.The whole structure thickness is 11.95 mm.The thickness of composite patches is 4.2 mm,the thickness of honeycomb dielectric layer is 7.6 mm,and absorption.The absorption bandwidth reaches 13.5 GHz(4-17.5 GHz).The loss mechanism of the whole structure is analyzed.The resonant peaks of composite patches at 5 GHz and 16 GHz effectively broaden the absorption bandwidth of the whole structure at low and high frequencies.In addition,a composite patch-metal FSS structure is designed.The thickness of the whole structure is 6.65 mm.The physical structure is fabricated and tested.The absorption peak is at 3.1 GHz and the bandwidth of-10 dB is 1.0 GHz(2.7-3.7 GHz).Finally,the patterned design of carbon nanotube composites with 4% mass fraction was carried out,and the variation of pattern size,material thickness and honeycomb thickness was investigated.A composite structure with an overall thickness of about 2.7 mm was obtained.The measured absorption peak was at 7.37 GHz and the bandwidth below-10 dB reached 2.42 GHz(6.3-8.72 GHz).In summary,three kinds of absorbing structures have been designed based on carbon nanotubes/silicone rubber composites according to the requirements of absorbing strength,absorbing bandwidth,mass and thickness of absorbing materials.The absorbing laws of these three structures are explored,and the absorbing mechanism of composite structures is analyzed from the aspect of loss distribution. |
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